(1) Field of the Invention
The present invention relates to intravascular prostheses, delivered transarterially or transvenously, for the occlusion of cardiac defects. Such defects include the patent ductus arteriosus, the ventricular septal defect and the atrial septal defect.
(2) Description of the Related Art
U.S. Patents: KING et al, U.S. Pat. No. 3,874,388, SIDERIS, U.S. Pat. No. 4,917,089.
Publications: Rashkind--Circulation--vol 67, No. 4, April 1983.
Patent ductus arteriosus is an important vessel for the fetus, because a large percentage of the cardiac output is bypassing the lungs through the ductus. However, the ductus after birth is constricted after exposure to oxygen in the majority of children. Patency of ductus arteriosus after birth is common in premature babies (30%), and uncommon in term babies (&lt;1%). Persistence of the ductus arteriosus is associated with left to right shunt with increased volume of blood crossing from the aorta to the pulmonary artery and the lungs. Left to right shunt can cause deterioration of the lung disease in premature infants, congestive heart failure in infancy and pulmonary vascular obstructive disease in older children. Patency of ductus arteriosus carries the risk of infection (endarteritis or endocarditis), in all ages. For this reason occlusion or surgical ligation of the ductus arteriosus is recommended in all cases.
Surgical ligation or division carries low risk especially in older children. However, it is always associated with significant morbidity because of the need of thoracotomy, general anesthesia, placement of chest tubes, intensive care. The discomfort and the expense are significant. For these reasons attempts have been made for the transcatheter occlusion of patent ductus arteriosus.
Ventricular septal defect is the commonest heart defect. It causes congestive heart failure to a number of children and it often requires surgery in early life. Unfortunately most of the defects do not have adequate rim and therefore are not amenable to umbrella occlusion. However, some of them (muscular VSDs) could be closed provided that a device existed to be applicable in small children and adjustable for the ventricular septal thickness.
Historically, the first transcatheter occlusion of PDA was performed by Posner in Germany transarterially, utilizing an Ivalon foam plug. The method has been used primarily by German and Japanese investigators in adults and older children. It requires a large femoral artery for the entry and it is associated with significant arterial complications.
Sporadic reports about detachable balloons, special bags, or metals have followed.
KING and MILLS invented a Double Disk device, (U.S. Pat. No. 3,874,388) for the occlusion of intracardiac defects and primarily ASDs. The device was bulky, requiring a 23 F introduction. Modifications on the same principle were made by others. The most successful one was the one by RASHKIND, commercialized by BARD. The device employs two discs on the same catheter. The discs are made by polyurethane foam and a metal skeleton. They are connected through a complex release mechanism to the main catheter. The distal disk is released in the arterial side of the ductus and the proximal disk in the pulmonary artery side, in case of transvenous PDA occlusion. The RASHKIND device requires a large introduction (11 F) for PDAs larger than 4 mm and an 8 F introducing sheath, for small PDAs. Therefore, the method has not found application in small children with large communications. Indeed this is the group where occlusion is most urgent. Furthermore, it is not applicable to long and tubular PDAs or even very short ones. Because of the large introducing sheath, there is often the need of dilation of the small ductus by angioplasty balloons prior to the occlusion. The incidence of residual shunts is significant, especially in large PDAs. A common objection to the method is the persistence of the ductal channel despite its occlusion, since the device is only obstructing the narrow part of the ductus.
Another recent modification of the KINGS and MILLS device was the "Clumshell" device. It was applied successfully for ASD, PDA and VSD occlusion. However, it was withdrawn because of wire fracture. It was quite bulky, requiring an 11 F introduction and therefore was not applicable in small children.
In 1990 a patent was issued for the "Buttoned Device For The Occlusion Of The Intracardiac Defects" (U.S. Pat. No. 4,917,089). This device is made by two independently introduced disks that are eventually buttoned across a defect. It requires a small sheath (7-8 F) for introduction and it can be used in small children. However, the distance between the two disks is predetermined since the button loop has a length of 2-4 mm for the ASD application. Therefore, what it can be applicable for an ASD occlusion cannot be used for a long "tubular" PDA occlusion. Ventricular septum has a different thickness than the atrial septum and therefore an ASD occluding buttoned device cannot be used for a ventricular septal defect occlusion.